1. Technical Field of the Invention
This invention relates generally to the field of hepatitis C virus (HCV) and, more specifically, to the discovery of an immunologically important motif in the E2/NS1 region.
2. Brief Description of Related Art
Hepatitis C virus (HCV) has been identified as the major causative agent of post-transfusion non-A, non-B hepatitis (NANBH). Materials and methods for obtaining the viral genomic sequences are known. See, e.g., PCT Publ. Nos. WO89/04669, WO90/11089, and WO90/14436. For general information about HCV, see Houghton et al. (1991), Hepatology 14:381–388.
Molecular characterization of the HCV genome indicates that it is a RNA molecule of positive polarity containing approximately 9,500 nucleotides comprising a long translational open-reading frame (ORF) that could encode a large polypeptide of approximately 3000 amino acids (aa) beginning with the first in-frame methionine codon. A hypervariable domain located at the amino terminus of the putative envelope glycoprotein E2/NS1 (also called E2) has been located, see PCT Publ. No. WO93/016126; Weiner et al. (1991), Virology 180:842–48; Weiner et al (1992), Proc. Natl. Acad. Sci. USA 89:3468–72; Weiner et al. (1992), Vaccines 92:303–08, Cold Spring Harbor Laboratory.
As observed for other RNA viruses, there is a substantial fluidity of the HCV genome resulting from an error-prone replicase and the absence of repair mechanisms that operate during DNA replication. Even in a single infected individual, the HCV genome does not exist as a homogeneous species. Rather, it exists as a quasi-species distribution of closely related but nevertheless heterogeneous genomes. Martell et al. (1992), J. Virol. 66:3225–3229. In addition, the process of host selection and adaptation of a rapidly mutating genome has led to the evolution of many distinct (yet still fluid) HCV genotypes. At least four different HCV genotypes can be distinguished according to the actual degree of nucleotide and amino acid relatedness of full length sequences, and additional different genotypes have been identified based on partial sequences. Mori et al. (1992), Biochem. Biophys. Res. Commun. 183:334–342; Chan et al., (1992), J. Gen. Virol. 73:1131; Cha et al. (1992), Proc. Natl. Acad. Sci. USA 89:7144–7148.